Method for synchronously separating and recovering phosphate, metal and complexing agent from chemical copper plating wastewater by using self-driven electrochemical system

Abstract

The invention relates to a method for synchronously separating and recovering phosphate, metal and a complexing agent from chemical copper plating wastewater by using a self-driven electrochemical system, and belongs to the technical field of crystallization. According to the method, Cu (II) / Fe (s) chemical potential difference driving is utilized, copper in the chemical copper plating wastewater is synchronously separated and recycled under the condition of zero external source energy supply, and meanwhile recycling of organic ligands is achieved. Aiming at the interference of Cu-EDTA in actual wastewater, the transmembrane migration of Cu (II)-EDTA and EDTA ligands is effectively inhibited through a pH regulation anion form coupling monovalent anion exchange membrane strategy, and the selective separation and recovery of phosphate radicals are realized. The system can adapt to a real chemical plating wastewater pH range, can stably operate in a real wastewater experiment, and successfully recovers high-purity copper elementary substance and high-crystallinity blue iron ore. The invention shows that the electrochemical-crystallization coupling technology provides a feasible path for multi-resource cyclic utilization of wastewater.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of crystallization, in particular to a method for simultaneously separating and recovering phosphates, metals and complexing agents from chemical copper plating wastewater by using a self-driven electrochemical system. BACKGROUND

[0002] Metal-containing wastewater has significant resource recovery value, but existing researches mostly focus on the extraction of metal ions, while the synergistic recovery of other key components (such as organic complex and phosphorus compound) in wastewater is generally ignored. This research limitation is particularly prominent in the field of chemical plating, where simple oxidation or biochemical treatment methods are commonly used to dispose of these substances, resulting in serious resource waste.

[0003] Chemical copper plating process has been widely used in precision electronic manufacturing and other fields due to its excellent deposition quality and good uniformity of the plated layer. This process uses hypophosphite as a reducing agent, and during plating and rinsing, wastewater containing high concentrations of copper ions (50-500 mg / L) and phosphorus pollutants (100-10 000 mg / L) is generated. These components pose environmental risks: copper ions have significant biological toxicity, while phosphorus, as a limiting nutrient element, can cause water eutrophication. More paradoxically, copper is an important metal resource, and phosphorus is a non-renewable strategic resource, with global reserves facing depletion crisis. The current treatment mode actually creates a dilemma of coexistence of pollution control and resource loss.

[0004] One of the challenges in the resource recovery of chemical plating wastewater is the complex of high concentration chelating ligand (such as ethylenediaminetetraacetic acid, EDTA) and heavy metal (such as Cu-EDTA) in wastewater. These high solubility and difficult-to-degrade metal-organic complexes have strong resistance to traditional treatment technologies such as adsorption, chemical precipitation and ion exchange. Therefore, various advanced oxidation processes (AOP), including ozonation, Fenton reaction and electrochemical oxidation, are used for the treatment and recovery of metal-organic complexes. These oxidation methods can release Cu 2+ by destroying the molecular structure of EDTA, but have obvious defects: the oxidation process leads to the decomposition of EDTA into metastable nitrogen-containing intermediates (such as EDMA, IMDA, etc.), which not only cannot recover the organic ligand, but also may exacerbate water eutrophication and complicate the traditional denitrification process. At the same time, recent studies on the treatment mechanism of Cu-EDTA show that when the cathode potential is more negative than the standard reduction potential of Cu(II) / Cu(0), the removal of Cu(II)-EDTA is mainly due to the direct cathodic reduction process (Formula 1), rather than relying on the high-energy oxidation mechanism. Therefore, electrodeposition technology can achieve the synergistic recovery of metals and organic ligands, and has become the mainstream technology for metal recovery. However, traditional electrochemical methods are high in cost and energy consumption, making them difficult to be widely applied.

[0005] Cu(II)-EDTA + 2e - → Cu(0) + EDTA Equation (1), To address the problem of high energy consumption, researchers have proposed a metal recovery system based on spontaneous potential in recent years, which recovers metals by constructing a spontaneous redox reaction and generates electricity at the same time. For example, in the field of uranium (U) recovery, by spatially decoupling the uranium adsorption reduction reaction and the iron oxidation reaction, a sacrificial iron anode primary battery system can be constructed to achieve spontaneous extraction and recovery of uranium. Sun et al. designed an electrochemical-permeation system based on a primary battery Fe(s) / Cu 2+ (aq) for the simultaneous recovery of Cu 2+ metals and water resources from wastewater. On this basis, Sun designed a nickel nanoparticle functionalized photoanode to replace the iron anode, which recovers metals and water resources from copper-containing wastewater using solar energy. However, these systems only explore the performance in pure metal ion systems, without considering the influence of metal-organic complexes, and also without realizing the recovery of phosphates and other substances.

[0006] In addition to metal-organic complexes, the characteristic pollutants of electroless plating wastewater also contain high concentrations of phosphates (TP: 100-10 000 mg / L). There is currently no report on the existing technology of the study of blue vitriol crystallization for electroless plating wastewater, and the crystallinity of blue vitriol is generally low.

[0007] 3Fe 2+ +2PO4 3- +8H2O → Fe3(PO4)2·8H2O Equation (2). SUMMARY

[0008] To solve the technical problems of high energy consumption, high reagent consumption and low resource recovery rate in the traditional oxidation-precipitation method for treating electroless plating wastewater, the present application provides a method for simultaneously separating and recovering phosphates, metals and complexing agents from electroless copper plating wastewater using a self-driven electrochemical system. The metal recovery system based on spontaneous potential provides a new idea for solving the simultaneous recovery of phosphates: Fe 2+ released by the sacrificial iron anode during the oxidation process can migrate across the membrane and form high-value-added blue vitriol (Fe3(PO4)2·8H2O) crystals under controlled conditions (Equation 2). The crystallization method is considered an ideal approach for wastewater phosphorus recovery because the product is easy to separate and has great value. Because iron salts are relatively inexpensive and easy to obtain, the theoretical pH range for the formation of blue vitriol is relatively wide (5-10), so the reagent input required to synthesize blue vitriol crystals is relatively small. Compared with the struvite crystallization method, it is considered an economical and feasible method for phosphorus recovery. At the same time, blue vitriol is a relatively stable phosphorus-iron compound (K sp 10-25 -39 The chemical plating wastewater has high phosphorus content (28.5%, P2O5) and can be used as a raw material for producing phosphate fertilizer and has great market value in high-end applications (such as lithium battery positive electrode material synthesis raw material).

[0009] The application aims to provide a method for simultaneously separating and recovering phosphate, metal and complexing agent from chemical plating copper wastewater by using a self-driven electrochemical system, and the method comprises the following steps: Providing a self-driven electrochemical system configured with a monovalent anion exchange membrane and chemical plating wastewater; The self-driven electrochemical system comprises a cathode chamber provided with a cathode and an anode chamber provided with an anode, and a monovalent anion exchange membrane arranged between the cathode chamber and the anode chamber, and a current collector is arranged on the adjacent side of the anode and the cathode, and the current collectors are connected by a metal wire to form a primary cell structure; the anode is an iron sheet; The chemical plating wastewater is used as a cathode electrolyte, and a NaCl solution is used as an anode electrolyte; The spontaneous chemical potential difference between the anode iron sheet and the free Cu 2+ in the cathode electrolyte is utilized, and at the same time, the anion form difference of the phosphate, [CuEDTA] 2- and EDTA 2- in the chemical plating wastewater under the action of the monovalent anion exchange membrane is utilized to realize the directional migration of the phosphate to the anode chamber, so that H2PO4 - is combined with Fe 2+ at the anode to generate blue vitriol, thereby realizing the recovery of the phosphate; the free Cu 2+ in the cathode electrolyte is precipitated in the form of elemental copper at the cathode to realize the recovery, and EDTA is precipitated under acidic conditions to realize the recovery.

[0010] In the application, all components in the self-driven electrochemical system are compressed into a stack by using acrylic end plates and glass-reinforced nylon screws, and a CNC milling machine is used to accurately cut flow paths and holes on each material.

[0011] In some embodiments of the application, the chemical plating wastewater comprises a CuEDTA complex, free Cu 2+ and phosphate anions.

[0012] In some embodiments of the application, the concentration of the CuEDTA complex is 1-10 mM.

[0013] In some embodiments of the application, the concentration of the free Cu 2+ is 3-30 mM, and the total phosphorus content is 8-80 mM.

[0014] In some embodiments of the application, the pH value is 3-6.​

[0015] In some embodiments of the application, the dissolved oxygen concentration of the catholyte is ≤ 2.0 mg / L.

[0016] In some embodiments of the application, the cathode is a stainless steel sheet.

[0017] In some embodiments of the application, the current collector is a titanium current collector.

[0018] In some embodiments of the application, the concentration of the NaCl solution is 9 mM, and the pH of the anolyte is 6.

[0019] In some embodiments of the application, the reaction time is greater than or equal to 6 h. Acidic conditions: the pH value is controlled below 3.0, and in the application, EDTA (ethylenediaminetetraacetic acid) is used in its free acid form (H4Y) which has very low solubility in water. By adding sulfuric acid to the treated solution, the pH value is controlled below 3.0, which promotes the combination of hydrated hydrogen ions (H + ) and EDTA anions to form white EDTA acid precipitate which is difficult to dissolve in water, and the separation and recovery can be achieved by filtration.

[0020] The mechanism of resource synergistic recovery by the self-driven electrochemical crystallization method of the application: in the reaction process, the anode undergoes the reaction of Fe 0 oxidation to Fe 2+ (the formula (7)), which has more thermodynamic advantages than the reaction of Fe 0 oxidation to Fe 3+ ; the cathode undergoes the reaction of Cu 2+ reduction to Cu 0 . According to the overall reaction shown in formula (8), the theoretical open circuit voltage (OCV) of the system under standard conditions is 0.78 V, which provides a driving force for the transmembrane migration of phosphate. The application uses a monovalent anion exchange membrane M-AEM, and the selective migration of phosphate is realized by the difference in anion form of H2PO4 - , [CuEDTA] 2- and EDTA 2- , so that the phosphate combines with Fe 2+ at the anode to form the blue vitriol and is recovered.

[0021] Theoretical analysis based on the Nernst equation shows that the concentrations of Fe 2+ and Cu 2+ are the key factors affecting the open circuit voltage (OCV) of the system. In the actual reaction process, the concentration of Cu 2+ will continuously decrease with the reduction reaction, and in the actual wastewater, the concentration of Cu 2+The concentration also fluctuates, and its dynamic changes significantly affect the system's driving force. Meanwhile, homogeneous nucleation of vivianite requires Fe... 2+ The ion activity product (IAP) with phosphate reaches the solubility product (K). sp The Fe content is 5-10 times that of Fe, therefore, this invention achieves this by reducing the volume of the anolyte. 2+ Concentration enrichment. It should be particularly noted that, due to Fe... 2+ With OH - The precipitation reaction of anions such as phosphate, and Fe in the anolyte 2 The concentration of ⁺ exhibits a dynamic change pattern of first increasing and then decreasing.

[0022] The technical solution of the present invention has the following advantages compared with the prior art: This invention proposes an autonomous electrochemical-crystallization system (SECS) based on chemical potential gradient. Figure 1 This system is designed to address the challenges of synergistic treatment and resource recovery of metal complexes and phosphates in chemical plating wastewater. It utilizes the oxidation reaction at the iron anode to drive the oxidation of Cu(II) (including free Cu) in the cathode chamber. 2+ The system achieves spontaneous reduction and recovery of phosphate (including complexed Cu-EDTA) without requiring additional electrical energy input. Through the spontaneous chemical potential difference between Fe(s) and Cu(II), the system simultaneously enables the directional migration of phosphate to the anode chamber and its reaction with Fe dissolved from the anode. 2+ This process combines to form highly crystalline lapis lazuli and recover phosphate. This invention targets [CuEDTA]. 2- and EDTA 2- To address the problem of anion migration interference, a synergistic strategy of regulating anion speciation coupled with a monovalent selective anion exchange membrane (M-AEM) was proposed. This successfully suppressed the migration of EDTA and its metal complexes into the anode chamber, resulting in the successful formation of high-grade lapis lazuli at the anode. Subsequently, the effects of key parameters such as cathode material selection and dynamic pH changes at both the anode and cathode on resource recovery efficiency were systematically investigated. Finally, the SECS system was used to treat real electroless copper plating wastewater, validating the system's practical application potential. This invention provides important insights into the challenges of synergistic resource recovery from electroless plating wastewater and has significant practical implications for achieving a circular economy.

[0023] This invention utilizes an autonomous electrochemical-crystallization system, relying on the spontaneous electron flow of Cu(Ⅱ) / Fe(s), to achieve the simultaneous separation and recovery of multiple components, including metals, phosphates, and complexing agents, from chemical plating wastewater.

[0024] A core breakthrough of the SECS is the reconfiguration of the material flow of pollutants in complex electroless wastewater. Specifically, (1) M-AEM is used instead of ordinary AEM, combined with pH adjustment of ion valence, to achieve selective migration of phosphate and recovery in the form of vivianite; (2) waste iron that many industries may consider as waste is converted into well-crystallized vivianite, which can be used as a phosphorus-iron fertilizer for resource utilization; (3) compared with traditional chemical precipitation and electro-reduction methods, this method uses various industrial waste (such as solid metal waste) for wastewater treatment, improving the sustainability of the process.

[0025] The SECS has multifunctionality and high flexibility, and can be extended to the recovery of high-value metals (not only copper), and can effectively intercept various ligands such as citric acid and metal-organic complexes in electroless wastewater. Although the SECS is only demonstrated on a laboratory-scale prototype, it embodies an innovative system design that can recycle, recycle and integrate valuable resources in complex wastewater, and promotes the transition from a linear economy to a circular economy.

[0026] In summary, the present application provides the development of a new sustainable process, which provides an efficient and environmentally friendly solution for the resource utilization of complex wastewater, and has important practical significance for realizing a circular economy. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to make the content of the present application more easily understood, the present application will be further described in detail below according to specific embodiments of the present application and in conjunction with the drawings, wherein, Figure 1 is a device diagram of the self-driven electrochemical system of the present application.

[0028] Figure 2 is a physical diagram of the self-driven electrochemical system of the present application.

[0029] Figure 3 is a mechanism schematic diagram and a potential diagram of the present application. Among them, (a) is a mechanism schematic diagram of the SECS system for simultaneously recovering copper, phosphate and EDTA from wastewater; (b) is the relationship between the anode potential (E(Fe 2+ / Fe)) and the Fe 2+ concentration (the shaded area is the potential fluctuation range under actual operation conditions); (c) is the relationship between the cathode potential (E(Cu 2+ / Cu 0 ) and the Cu(II) concentration.

[0030] Figure 4Resource recovery performance of different types of AEM system in the present application. (a) Macro-morphology of anode deposit of standard AEM system (mixed solid of light blue and red copper) and its SEM-EDS analysis results; (b) Macro-morphology of anode deposit of M-AEM system (single light blue solid) and its SEM-EDS characterization; (c) Comparison of XRD patterns of deposits of different membrane systems; (d) Distribution of Cu-EDTA forms with pH change based on Visual MINTEQ model; (e) Simulated distribution characteristics of phosphate forms with pH change; (f) Comparative analysis of total interception rate of EDTA and Cu(II) recovery rate of AEM and M-AEM systems.

[0031] Figure 5 Mechanism analysis of the regulation of cathode liquid pH on the performance of the system. (a) Purity and apparent morphology of recovered copper under different initial pH conditions; (b) Change of cathode pH value during operation under different initial pH conditions; (c) Phosphorus recovery efficiency under different initial pH conditions; (d) Final T-EDTA interception rate under different initial pH conditions.

[0032] Figure 6 Effect of different cathode materials (SS201, SS316, PCC, CFP) on resource recovery performance of SECS system in the present application; (a) Comparison of phosphorus recovery efficiency of different cathode materials, inset: comparison of purity of recovered copper of different cathode materials; (b) Linear sweep voltammetry curves of different cathode materials; (c) Change of phosphorus recovery efficiency of SS201 system under different initial cathode pH values, inset: change of T-EDTA interception rate of SS201 system under different initial cathode pH values; (d) Purity and corresponding morphology of cathode copper deposit obtained under different initial cathode pH conditions when SS201 cathode is used.

[0033] Figure 7 Effect of initial pH of anode on crystallization in the present application. (a) Change curve of anode liquid pH with reaction time; (b) XRD spectrum of formed vivianite under different initial pH conditions; (c) Change of intensity of characteristic peak (020) of vivianite and comparison of product color; (d) Change of phosphate removal rate and mobility of the system.

[0034] Figure 8 Application potential evaluation of SECS in the present application. (a) Copper and phosphorus recovery performance and T-EDTA interception efficiency in the cyclic experiment; (b) Dynamic change of open circuit voltage (OCV) and Faraday efficiency during the cyclic experiment; (c) Change process of copper / phosphorus concentration and OCV with time in the actual wastewater treatment process; (d) Economic benefit analysis of resource recovery process of SECS.

[0035] Figure 9 is the batch experimental current change of the present application. DETAILED DESCRIPTION

[0036] The present application is further described below in conjunction with the accompanying drawings and specific examples so that it can be better understood and carried out by those skilled in the art. The examples are not intended to limit the present application.

[0037] The calculation formula of the material and substance recovery used in the present application 1、The standard anion exchange membrane and monovalent anion exchange membrane used in the present application are purchased from Japan ASTOM, stored in 1M NaCl solution, and soaked in deionized water for 12 h before the experiment. The porous activated carbon cloth and carbon fiber paper are purchased from Taiwan, China, and treated with ultrasonic in anhydrous ethanol for 30 min and washed with deionized water to remove ash before use. The iron sheet and stainless steel sheet are purchased from China Merck, and polished with sandpaper (400 - 1000 mesh) before use.

[0038] 2、In the present application: (1) The calculation formula of the removal rate of phosphate and T-EDTA interception efficiency is as follows: (1) In the formula, C 0,i and C c,i represent the initial concentration and final concentration of phosphorus and T-EDTA in the cathode chamber, respectively, and the unit is .

[0039] (2) The calculation formula of the phosphorus recovery efficiency is: (2) In the formula, C a,P represents the final concentration of phosphorus in the anode chamber, C 0,P represents the initial concentration of phosphorus in the cathode chamber, and C c,P represents the final concentration of phosphorus in the cathode chamber, and the unit is .

[0040] (3) The calculation formula of the copper recovery efficiency is: (3) The calculation is by nitric acid digestion of the sediment, and the copper concentration is determined by inductively coupled plasma emission spectrometry, wherein: C 0,Cu is the initial concentration of copper in the catholyte (mol / L); C dig,Cu is the copper concentration in the digestion solution ( ); V0 is the volume of the catholyte (L); V dig is the volume of the digestion solution (L).

[0041] (4) The purity of the recovered copper is defined as the mass fraction of metallic copper in the cathode deposit: (4) The determination is carried out by hydrochloric acid digestion of the deposit. Among them: is the molar mass of copper (64 g / mol); C dig,Cu is the copper concentration in the digestion solution (g / L); V dig is the volume of the digestion solution (L); m dep is the total mass of the dry cathode deposit.

[0042] (5) The Faraday efficiency (FE) is defined as the total amount of electric charge consumed by the cathode copper reduction reaction and the anode reaction (5) where V0 and V t represent the volume of wastewater (i.e. cathode electrolyte) at time 0 and t, respectively; I is the current (a function of time t); C Cu,0 and C Cu,t are the copper concentrations at the corresponding time; F is the Faraday constant.

[0043] (6) The general form of the Nernst equation is shown in equation (6), which can be simplified to equation (7) at room temperature (298 K): (6) (7) where E 0 (M n+ / M) represents the standard electrode potential of a given electric pair under standard conditions, E(M n+ / M) is the electrode potential under specific conditions, R is the gas constant, T is the absolute temperature, n is the number of electron transfers, and F is the Faraday constant.

[0044] Example 1 This example provides a recovery method for simultaneously separating and recovering phosphates, metals and complexing agents from chemical copper plating wastewater using a self-driven electrochemical system, as shown below: I. Self-driven electrochemical system: The self-driven battery device is as shown in Figure 1 Specifically, it includes: one (5 cm x 5 cm) activated carbon cloth electrode / stainless steel sheet as the cathode, one (5 cm x 5 cm) high-purity iron sheet as the anode, a standard anion exchange membrane or a monovalent anion exchange membrane placed between the cathode and anode chambers (5 cm x 5 cm x 0.2 cm) made of rubber material, titanium current collectors are added on the adjacent side of each electrode, and metal wires are used to connect the current collectors to form a primary battery structure. The device is shown in Figure 2All components were compressed into a stack using acrylic endplates and glass reinforced nylon screws, with flow channels and holes precisely cut into each material using a CNC mill.

[0045] II. Simultaneous recovery of phosphate, metal and complexing agent from electroless copper plating wastewater by self-driven electrochemical system, comprising the following steps: According to the concentration of each component in the actual electroless plating wastewater, 50 mL of 1 mM Cu(II)-EDTA (using Na2CuEDTA and water to configure 1 mM Cu(II)-EDTA), 3 mM CuSO4 and 8 mM total phosphorus (mainly including the sum of the concentration of phosphate anion concentration of 8 mM) simulated wastewater as catholyte, without introducing too many impurity ions, the ratio of phosphoric acid and dihydrogen phosphate in the catholyte was changed to regulate the pH of the catholyte, and the total phosphorus concentration was unchanged. 25 mL of deionized water was used as an anolyte (9 mM NaCl was added to make it similar to the conductivity of the catholyte), and the pH of the anolyte was adjusted to 6.0 by adding 10 mM H2SO4. During the experiment, the cathode and anode were connected using an electrochemical workstation (Chenhua CHI650E, China) and the I-t data was recorded. In order to make the catholyte and anolyte circulate in the cathode chamber and anode chamber respectively, a peristaltic pump was used to pump the solution into the chamber at a flow rate of 5 mL / min, and the reaction lasted for 6 h. During the reaction, the catholyte was purged with nitrogen to maintain the dissolved oxygen concentration below 2.0 mg / L. The solid samples formed on the electrodes were freeze-dried under vacuum conditions for further characterization, and the results showed that the cathode obtained metal elemental copper product and the anode obtained ferrous phosphate product. All experiments were repeated at least three times.

[0046] Analysis of experimental results To verify the thermodynamic feasibility of the system, the Nernst equation was used to simulate the variation of cathode potential E(Cu 2+ / Cu 0 ) and anode potential E(Fe 2+ / Fe) with the corresponding ion concentration (b and c in Figure 3 ). The simulation results show that the cathode potential decreases with the decrease of Cu 2+ concentration, and the anode potential decreases due to the accumulation of Fe 2+ . The anolyte and catholyte were tested by ICP, and the experimental monitoring data showed that the Fe 2 ⁺ concentration in the anolyte reached a peak of about 1.1 mM after 2 h of reaction, and the Cu 2+ concentration in the catholyte decreased to about 10 -10 mM after 6 h of reaction. Even under this extreme condition, the system still maintains a theoretical OCV of 0.44 V, fully demonstrating its ability to continuously drive the transmembrane migration of phosphate.

[0047] During the experiment, the initial cell voltage was about 0.56 V, corresponding to a current density of 0.4 mA / cm 2 . As the reaction proceeded, the voltage dropped to 0.47 V and remained in a relatively stable change trend. This phenomenon can be attributed to the double dynamic balance of the cathode and anode: on the one hand, the Cu 2+ concentration in the cathode solution decreased significantly, but on the other hand, the Fe 2+ concentration in the anode solution also dropped to a low level below 0.01 mM due to the continuous precipitation of the blue vitriol. This synergistic effect maintained the potential difference balance of the system, making the output voltage tend to be stable. Finally, the system current density maintained a stable level of 0.07 mA / cm 2 , which confirmed the continuous effectiveness of the self-driven electron transfer mechanism during the reaction process.

[0048] Cu 2+ + 2e - → Cu 0 E 0 = +0.34 V vs. SHE Equation (6), Fe 2+ + 2e - → Fe 0 E 0 = -0.440 V vs. SHE Equation (7), Fe 0 + Cu(II) → Cu 0 + Fe 2+ E 0 = 0.78 V Equation (8), (1) Comparison of different AEM systems By using ordinary anion exchange membrane AEM and M-AEM for comparison experiments, the results are as follows: 1) It was found that ordinary anion exchange membrane cannot effectively block the transmembrane migration of CuEDTA 2- . Although this membrane can limit the Fe 2+ produced by the oxidation of the anode to enter the cathode chamber, avoiding its complexation with EDTA, it was observed that elemental copper appeared in the anode deposit. As shown in Figure 4 (a), the cathode deposit is a uniform and dense metal copper, while the anode deposit contains both the characteristic light blue color of blue vitriol and the red color of elemental copper; SEM analysis shows that the anode deposit has a layered structure of blue vitriol, but EDS detects obvious enrichment of copper element. As shown in Figure 4 (c), XRD analysis further confirms that there are both elemental copper (Cu 0 ) and the characteristic diffraction peaks of blue vitriol in the anode deposit. At the same time, Figure 4Figure 3 shows that 72.3% of total EDTA (the sum of the concentrations of EDTA ligand and Cu-EDTA complex) in the catholyte migrated across the membrane. These results directly demonstrate that CuEDTA 2- will cross the membrane into the anode chamber and be reduced to elemental copper at the anode.

[0049] 2) The experimental results show that the transmembrane migration of CuEDTA 2- may affect the reaction system in multiple ways. On the one hand, due to the reduction and deposition of CuEDTA at the anode, the purity of the phosphate product (blue iron ore) is reduced (as shown in Figure 4 (a) and (c) of Figure 2). On the other hand, the transmembrane transport of CuEDTA 2- reduces the content of Cu(II) in the cathode and may also compete with the transmembrane mass transfer of phosphate. Compared with the control group without EDTA and containing only 4 mM free Cu 2+ , the recovery rate of Cu(II) in the cathode is reduced by 22.8%, and the recovery rate of phosphorus is reduced by 20.6%. It should be noted that in the standard anion exchange membrane system, the migration amount of free Cu 2+ is very low (copper content in anode deposit <0.1%). These results collectively show that the migration of Cu-EDTA is a key factor leading to the decline in system performance, and a more optimized membrane separation strategy needs to be developed to solve this problem.

[0050] 3) To control the transmembrane migration of Cu-EDTA, the present application proposes a strategy based on anion form coupling M-AEM to achieve selective migration of phosphate. Specifically, as shown in Figure 4 (d) of Figure 3, within the pH range of 4.0-6.0, Cu-EDTA mainly exists in the form of [CuEDTA] 2- (>76% share), EDTA mainly exists in the form of [H2EDTA] 2- , and the dominant form of phosphate is monovalent charge H2PO4 - (>93% share). This significant charge difference provides a theoretical basis for selective membrane separation. After using M-AEM, the total rejection rate of EDTA increased significantly from 27.7% to 85.6%, indicating the high rejection effect of M-AEM on multicharge ligands and complexes.

[0051] 4) The characterization results of the anode product further verify the effectiveness of the strategy. Compared with the conventional AEM system, the anode deposit of the M-AEM system presents a typical greenish color (as shown in Figure 4In the middle (b), EDS spectrum analysis did not detect obvious Cu element signal, and XRD diffraction pattern only showed the characteristic diffraction peaks of blue vitriol. Digestion analysis showed that the mass fraction of Cu in anode deposit decreased significantly from 6.1% in AEM system to 0.2%, which confirmed the effective blocking of M-AEM to Cu EDTA migration. At the same time, the system realized 94.2% of Cu(II) recovery rate and 58.5% of phosphorus migration rate, maintaining good resource recovery performance. In summary, by utilizing the charge characteristic difference of different anion species, the selective transport mechanism of M-AEM successfully realized the selective migration of phosphate in metal complex system, and finally achieved the synergistic recovery of copper, complexing agent and phosphorus resources.

[0052] (2) Effect of cathode liquid pH on system performance It is worth noting that the chemical composition of copper recovery products shows high sensitivity to cathode pH ( Figure 5 In the middle (a)). Under the condition of strong acidity with pH < 3.0, the cathode deposit showed the characteristic of brass color of typical copper element, and its purity was more than 90%. With the increase of pH, light blue Cu(OH)2impurities gradually appeared in the product.

[0053] The study showed that the pH regulation of cathode liquid had a significant antagonistic effect on the interception efficiency of T-EDTA and H2PO4 - transport behavior. When the initial pH of PCC cathode system increased from 2.5 to 4.0, the phosphorus recovery rate decreased significantly from 82.6% to 49.5% ( Figure 5 In the middle (c)), which was mainly due to the deprotonation of H2PO4 - to HPO4 2- under the condition of high pH in the cathode zone, which increased the transmission resistance of anion exchange membrane, and the copper precipitate formed under high pH environment reduced the electrochemical driving force. Contrary to the change trend of phosphorus recovery rate, the interception performance of M-AEM to T-EDTA increased with the increase of pH ( Figure 5 In the middle (d)), which was also due to the change of ion form and electrochemical driving force.

[0054] The experimental results showed that the pH in the cathode zone showed a rapid upward trend during the reaction ( Figure 5 In the middle (b)). This pH change had a double adverse effect on the synergistic recovery of multiple components: first, the neutral pH would lead to the conversion of H2PO4 - to HPO4 2- , thereby increasing the mass transfer resistance of phosphate through M-AEM; second, the free Cu 2+ under neutral pH condition was easy to form Cu(OH)2precipitate, which reduced the recovery efficiency of copper. Therefore, maintaining the stability of cathode liquid pH is a key control parameter to realize the efficient synergistic recovery of copper, phosphorus and complexing agent.

[0055] In this invention, the increase in cathode pH is mainly driven by two processes: (1) (1) Migration to the anode leads to pH changes in the cathode region; (2) Hydrogen evolution reaction at the cathode (HER: 2H) + + 2e - → H2↑) continuously consumes protons. Due to H2PO4 - pH changes caused by migration are an inherent characteristic of the system. This invention achieves stable control of the cathode pH by optimizing the selective inhibition of HER reaction kinetics by cathode materials.

[0056] (3) Influence of cathode material This invention systematically investigates the effects of porous carbon cloth (PCC), carbon fiber paper (CFP), stainless steel 201 (SS201), and stainless steel 316 (SS316) as cathodes on electrochemical resource recovery performance.

[0057] Experimental results show that when using SS201 and SS316 cathodes, the phosphorus recovery rate is significantly improved by 20.1% and 15.3% respectively compared to PCC cathodes. Figure 5 (a)). This performance improvement is mainly due to the effective pH regulation of the system by the stainless steel cathode. The pH in the cathode region can be maintained at around 6 when the reaction is terminated, while the carbon-based cathode, due to its higher specific surface area and three-dimensional porous structure, significantly promotes HER, resulting in a rapid increase in pH. Figure 5 (b) Further confirmation by linear sweep voltammetry revealed that SS201 exhibited the lowest HER activity, while SS316, due to its higher Ni content (>10 wt%), possessed relatively strong HER catalytic activity. Notably, all cathode materials showed T-EDTA rejection rates exceeding 80% and copper recovery rates exceeding 90%. Furthermore, ICP-MS analysis indicated that the concentrations of Fe and Ni ions dissolved from the stainless steel cathodes were below the detection limit of 0.5 ppm, ruling out the risk of heavy metal leaching.

[0058] The SS201 cathode system exhibits excellent pH tolerance. Experiments show that when the initial cathode pH increases from 2.5 to 4.0, the phosphorus recovery rate only decreases from 81.0% to 66.3%. Figure 5 (c) Meanwhile, the purity of the copper recovery product consistently remained above 90%, and high-purity metallic copper products (>90.0%) were consistently obtained under all test conditions. Figure 5 In the middle (d) section, the EDTA recovery rate was 63.6%. This is because the cathode pH of the SS201 cathode system was significantly lower than that of the PCC system under the same conditions. Under acidic conditions, Cu(II) in the system mainly exists as Cu. 2+The presence of Cu(II) in this form not only enhances the driving force for phosphate migration but also ensures the purity of the cathode deposit. Even in the later stages of the reaction, when Cu(II) exists primarily as CuEDTA, acidic conditions weaken the stability of CuEDTA, causing it to release more Cu. 2+ Therefore, when using SS201 as the cathode, the purity of its metallic copper product is significantly higher than that of the PCC system.

[0059] Taking into account resource recovery efficiency, pH control capability, and material stability, SS201 was determined to be the best cathode material for this system due to its optimal phosphorus recovery performance, lowest HER activity, and good chemical stability.

[0060] (4) Phosphate products This invention investigated the effect of the initial pH of the anolyte on the crystallization process. The results showed that, due to H₂PO₄… - Migration and hydrolysis of Fe 2+ The dynamic equilibrium of processes such as precipitation and crystallization, and the continuous change of anolyte pH during the reaction ( Figure 6 (a) When the initial anolyte is acidic (pH < 4.0), the anolyte pH gradually increases over time; while when the initial pH is close to neutral (5.0-7.0), it shows a trend of first slightly decreasing and then stabilizing. Under all conditions, the bulk catholyte pH remains stable in the range of 4.0-6.0. This pH dynamic is mainly governed by two processes: (i) Migration and subsequent hydrolysis consumption (ii) Fe released from the anode 2+ Phosphorus precipitates to form vivianite. These interaction mechanisms collectively shape the crystallization environment, ultimately influencing the kinetics and selectivity of phosphorus recovery in the vivianite form.

[0061] XRD analysis confirmed that all sediments exhibited a typical lapis lazuli crystal structure, with no impurity phases detected. Figure 6 (b)). However, as the initial pH increased from 4.0 to 7.0, the intensity of the (020) crystal plane diffraction peak decreased significantly ( Figure 6 In (b) and (c) the high pH conditions, the increased supersaturation index (SI) may promote secondary nucleation, thereby inhibiting the preferred growth of crystals. Furthermore, the high pH environment exacerbates the oxidation of Fe(II), causing the product color to gradually change from pale green (typical lapis lazuli) to muddy brown (Fe(III) precipitate). It is noteworthy that although changes in anolyte pH do not significantly affect phosphate migration efficiency, their crystallization recovery rate decreases significantly with increasing pH. Figure 6 (d)). Under lower pH conditions, phosphorus is mainly distributed as phosphorus. and The existence of this form leads to Fe 2+low utilization, slow crystallization kinetics, and ultimately poor phosphorus recovery. In contrast, near-neutral pH conditions enhance Fe 2+ oxidation and increase the risk of secondary nucleation.

[0062] (5) Practical application To evaluate the stability of the SESR system, the present invention conducted multiple batch experiments in a batch mode, with the catholyte being refreshed after each cycle while the anolyte remained unchanged. The system demonstrated robust operational stability over five consecutive cycles: the phosphorus recovery efficiency remained above 65.0%, the T-EDTA rejection rate stabilized at over 77.0% ( Figure 8 a); the average copper recovery rate reached 89.6%, corresponding to a cumulative copper recovery of 0.057 grams. The cell voltage remained stable at around 0.65 V ( Figure 8 b) during the operation. The electrons released by the anode iron were continuously consumed by the target electron acceptors (mainly free Cu 2+ and residual H + in the catholyte), achieving an ultra-high faradaic efficiency of over 90% ( Figure 8 b). The stable current density during the cycle process indicates that the passivation phenomenon of the iron electrode can be ignored, and Fe 2+ ( Figure 9 ) can be continuously released.

[0063] To verify the practical application potential of the SESR system, the present invention conducted experiments using real electroplating wastewater (water quality parameters are shown in Table 1). The cell voltage remained stable, and the phosphorus / copper concentration continuously decreased ( Figure 8 c) during the operation, ultimately recovering high-purity metallic copper and vivianite crystals ( Figure 8 d). The Fe / P molar ratio of the recovered vivianite (1.45-1.53) was highly consistent with the theoretical value of 1.5, as confirmed by EDS digestion analysis. Despite the presence of interfering ions in the actual wastewater, the system achieved a phosphorus recovery rate of 77.8% and a copper recovery rate of 90.3% ( Figure 8 e). The concentration of coexisting cations did not change significantly, while SO4 2- decreased slightly due to electromigration into the anode chamber, indicating that the SESR system still has excellent resource co-recovery performance for actual complex wastewater systems.

[0064] Table 1. Water quality of real electroplating copper wastewater

[0065] Economic analysis was conducted for the proposed SECS system to evaluate its economic feasibility for treating electroless plating wastewater and recovering copper and phosphate at commercial scale (Table 2). The results showed that the main cost components for treating each ton of wastewater were 5.18 $ for membrane material and 0.93 $ for other system components. The long-term cost of electrodes was effectively controlled due to the use of recyclable anode and cathode design. In terms of resource recovery, 0.24 kg of high-purity copper and 1.33 kg of blue vitriol could be produced from each ton of wastewater, which had a total value of 14.59 $ according to the current market price. The total cost for treating each ton of wastewater was 6.89 $, and the net profit was 7.70 $ after deducting the cost Figure 8 The results demonstrated that the SECS system had significant economic benefits in resource recovery, and further optimization of membrane material cost and other measures could further enhance the economic competitiveness of the system.

[0066] Table 2 Economic benefit analysis

[0067] Obviously, the above examples are merely examples for clarity and do not limit the embodiments. Based on the above description, those skilled in the art can make other different forms of changes or variations. Here, it is not necessary and impossible to exhaust all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for simultaneously separating and recovering phosphates, metals, and complexing agents from chemical copper plating wastewater using a self-driven electrochemical system: characterized in that, The method includes the following steps: A self-driven electrochemical system equipped with a monovalent anion exchange membrane and chemical plating wastewater are provided. The self-driven electrochemical system includes a cathode chamber with a cathode and an anode chamber with an anode, as well as a monovalent anion exchange membrane disposed between the cathode chamber and the anode chamber. Current collectors are disposed on adjacent sides of the anode and cathode, and the current collectors are connected by metal wires to form a galvanic cell structure; the anode is an iron sheet. The chemical plating wastewater was used as the cathode electrolyte, and NaCl solution was used as the anode electrolyte. Utilizing the free Cu in the anode iron sheet and cathode electrolyte 2+ The spontaneous chemical potential difference between them, and simultaneously, under the action of a monovalent anion exchange membrane, the phosphate and [CuEDTA] in the chemical plating wastewater... 2- and EDTA 2- The difference in anionic form enables the directional migration of phosphate into the anode chamber, allowing H2PO4 to... - At the anode and Fe 2+ The reaction generates lapis lazuli, enabling phosphate recovery; free Cu in the cathode electrolyte... 2+ Recovery is achieved by precipitating copper in the cathode, and EDTA is recovered by sedimentation under acidic conditions.

2. The method according to claim 1, characterized in that, The chemical plating wastewater includes CuEDTA complex and free Cu. 2+ And phosphate anions.

3. The method according to claim 2, characterized in that, The concentration of the CuEDTA complex is 1~10 mM.

4. The method according to claim 2, characterized in that, Free Cu 2+ The concentration is 3~30mM, and the total phosphorus content is 8~80mM.

5. The method according to claim 2, characterized in that, The pH value is 3~6.

6. The method according to claim 1, characterized in that, The dissolved oxygen concentration of the cathode electrolyte is ≤2.0 mg / L.

7. The method according to claim 1, characterized in that, The cathode is a stainless steel sheet.

8. The method according to claim 1, characterized in that, The current collector is a titanium current collector.

9. The method according to claim 1, characterized in that, The concentration of the NaCl solution is 9 mM, and the pH of the anolyte is 6.

10. The method according to claim 1, characterized in that, The reaction time is greater than or equal to 6 hours.

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